Method of feeding an inert gas and a system therefor

ABSTRACT

An inert gas is fed from an inert gas source to a piston-reciprocating compressor and compressed therein. The compressed gas is sent to a high-pressure storage tank. Pressure of the gas in the high-pressure storage tank is detected. When it reaches an upper limit, the piston-reciprocating compressor is stopped by a controller. At the same time, the gas is not fed from the inert gas source into the piston-reciprocating compressor and the gas from the compressor is released to outside. Meanwhile, when the pressure of the gas in the high-pressure storage tank reaches to a lower limit, the compressor starts. At the same time, the inert gas source is allowed to communicate with the compressor, and the gas which reaches to a desired density after the gas is released is sent from the compressor to the tank.

BACKGROUND OF THE INVENTION

The present invention relates to a method of compressing an inert gas sent from an inert gas source by a piston-reciprocating compressor and a system therefor.

An inert gas such as N₂ gas in a cylinder or produced in a N₂ gas generator is compressed by a booster compressor and forwarded to a high-pressure storage tank or part for use.

An ordinary piston-reciprocating compressor is generally employed as a booster compressor.

An inert gas is compressed by a piston-reciprocating compressor. When a supply valve between the inert gas source and the compressor is closed, pressure of a gas in a compression chamber on a piston becomes less than atmospheric pressure, so that air in a crank case under the piston likely invades into the compression chamber through the outer circumferential surface of the piston.

The inert gas is diluted by air, so that the density of the inert gas in the compression chamber is reduced.

To prevent such state, the supply valve is left open to let the inert gas source to communicate with the compression chamber even when the compressor stops, so that the compression chamber of the compressor does not become negative pressure.

However, in this case, a compressed gas in the compression chamber leaks into the crank case on the outer circumferential surface of the piston and is uselessly lost.

SUMMARY OF THE INVENTION

In view of the disadvantages above, it is an object of the invention to provide a method of preventing density of an inert gas in a high-pressure storage tank from lowering without losing the inert gas and a system therefor.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages will become more apparent from the following description with respect to embodiments as shown in accompanying drawings wherein:

FIG. 1 is a diagram showing one embodiment of the present invention; and

FIG. 2 is a diagram showing another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In an inert gas source 1 such as an inert gas generator of N₂ gas or an inert gas cylinder which is filled with N₂ under pressure, a sucking conduit 3 from an outlet hole 2 is connected to an inlet 10 of a piston-reciprocating compressor 9 having a piston 8 which reciprocates in a cylinder by a motor, via a supply valve 5 such as a two-way electromagnetic valve.

A release conduit 12 from an outlet 11 of the piston-reciprocating compressor 9 is connected to a high-pressure storage tank 14 via a check valve 13. Between the outlet 11 and the check valve 13, a relief valve such as a two-way electromagnetic valve 16 is connected to the conduit 12.

A pressure switch 23 of the high-pressure storage tank 14 is connected to a controller 22 via a connecting line 24.

A discharge valve 26 is connected to a discharge hole 25 of the high-pressure storage tank 14. To fill the high-pressure storage tank 14 with an inert gas, the supply valve 5 is opened with instructions from the controller 22, the relief valve 16 is closed after opening during a certain time, and the piston 8 is reciprocated in the piston-reciprocating compressor 9 by the motor 6.

The inert gas from the inert gas source 1 via the sucking conduit 3 is compressed by the piston-reciprocating compressor 9 and forwarded to the high-pressure storage tank 14 via the check valve 13. When pressure in the high-pressure storage tank 14 reaches an upper limit, the pressure switch 23 detects it. The controller 22 instructs the supply valve 5 to close and to stop the motor 6 to allow the piston-reciprocating compressor 9 to stop.

There is a little time lag between closing of the supply valve 5 and full stop of the piston-reciprocating compressor 9. During the time lag, a compression chamber on the piston 8 of the piston-reciprocating compressor 9 is decompressed to allow air to come into the compression chamber during a sucking stroke where the piston goes down. So air is mixed with the inert gas in the compression chamber and the sucking conduit 3, so that the density of the gas is reduced.

In this state, when the piston-reciprocating compressor 9 is operated again, density-reduced inert gas is sent to the high-pressure storage tank 14 within the time for recompression. So at the same time with or right after the recompression of the piston-reciprocating compressor 9, the supply valve 5 is opened by the instructions of the controller, so that high-density inert gas in the inert gas source 1 is sent to the piston-reciprocating compressor 9 and low-density inert gas in the release conduit 12 is released via the relief valve 16.

The low-density inert gas in the release conduit 12 is released for certain time. Thus, released inert gas from the piston-reciprocating compressor 9 becomes more than a certain density to make the controller 22 instruct to allow the relief valve 16 to close.

Hereinafter, the piston-reciprocating compressor 9 does not suck external air, but allows high-density inert gas from the inert gas source 1 to go to the high-pressure storage tank 14 via the check valve 13.

When an upper limit of pressure of inert gas in the high-pressure storage tank 14 is detected by the pressure switch 23, the supply valve 5 is allowed to close via the controller 22 and the motor 6 is stopped to allow the piston 8 to stop.

FIG. 2 shows another embodiment of the present invention, in which a three-way electromagnetic valve 28 is provided instead of the two-way electromagnetic valve 16 and the check valve 13 in FIG. 1.

To compress an inert gas in a piston-reciprocating compressor 9, a supply valve 5 in a sucking conduit 3 is opened and the three-way electromagnetic valve 28 of a release conduit 12 is opened for a certain time, and then closed.

When the pressure in a storage tank 14 reaches a certain level, the piston-reciprocating compressor 9 is stopped and a supply valve 5 is closed by a controller 22. The three-way electromagnetic valve 28 is still opened.

When the piston-reciprocating compressor 9 starts to compress a gas again, the supply valve 5 is opened and the three-way electromagnetic valve 28 is opened, so that low-density inert gas in the sucking conduit 3 and the compression chamber is released from the release conduit. When the density of the inert gas becomes a certain level, release is stopped by switching the three-way electromagnetic valve 28 to allow it to communicate with the storage tank 14.

The foregoing merely relates to embodiments of the invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein: 

1. A method of feeding an inert gas, comprising the steps of: feeding the inert gas from an inert gas source to a piston-reciprocating compressor; compressing the gas in the piston-reciprocating compressor; sending the compressed gas to a high-pressure storage tank; detecting pressure of the gas in the high-pressure storage tank when the pressure reaches an upper limit, to stop the piston-reciprocating compressor and feed of the inert gas into the piston-reciprocating compressor while the gas from the piston-reciprocating compressor is released to outside; and detecting pressure of the gas in the high-pressure storage tank when the pressure reaches to a lower limit, to start the piston-reciprocating compressor and to allow the inert gas source to communicate with the piston-reciprocating compressor while the gas is supplied from the piston-reciprocating compressor into the high-pressure storage tank when the gas reaches a desired density after the gas is released.
 2. A method according to claim 1 wherein the inert gas comprises N₂.
 3. A high-pressure inert gas feeding system comprising: an inert gas source feeding an inert gas; a sucking conduit having a supply valve and connected to the inert gas source; a piston-reciprocating compressor having an inlet and an outlet, the inlet being connected to the sucking conduit, said compressor compressing the inert gas; a release conduit connected to the outlet of the piston-reciprocating compressor and having a relief valve; a high-pressure storage tank connected to the release conduit and receiving the high-pressure inert gas; and a controller connected to the high-pressure storage tank, the supply valve of the sucking conduit, the piston-reciprocating compressor and the relief valve of the release conduit, said controller closing the supply valve, stopping the piston-reciprocating compressor and opening the relief valve to allow the gas to flow to outside when the pressure of the gas in the high-pressure storage tank reaches an upper limit, while said controller opens the supply valve, starting the piston-reciprocating compressor and shutting the relief valve after density of the gas reaches a desired level to allow the release conduit to communicate with the high-pressure storage tank when the pressure of the gas in the high-pressure storage tank reaches a lower limit.
 4. A system according to claim 3 wherein the inert gas comprises N₂.
 5. A system according to claim 3 wherein the relief valve comprises a two-way electromagnetic valve, said system further comprising a check valve in the release conduit between two-way electromagnetic valve and the high-pressure storage tank.
 6. A system according to claim 3 wherein the relief valve comprises a three-way electromagnetic valve.
 7. A system according to claim 3 wherein a pressure switch is connected to the high-pressure storage tank to detect the pressure of the gas in the high-pressure storage tank to send it to the controller. 